cp's OEIS Frontend

A249738 a(n) = 0 if n is 1 or a prime, otherwise, when n = A020639(n) * A032742(n), a(n) = the largest k < A032742(n) such that either k = 1 or A020639(k) >= A020639(n), where A020639(n) and A032742(n) are the smallest prime and the largest proper divisor dividing n.

%I A249738 #9 Dec 07 2014 18:11:20
%S A249738 0,0,0,1,0,2,0,3,1,4,0,5,0,6,3,7,0,8,0,9,5,10,0,11,1,12,7,13,0,14,0,
%T A249738 15,9,16,5,17,0,18,11,19,0,20,0,21,13,22,0,23,1,24,15,25,0,26,7,27,17,
%U A249738 28,0,29,0,30,19,31,11,32,0,33,21,34,0,35,0,36,23,37,7,38,0,39,25,40,0,41,13,42,27,43,0,44,11,45,29,46,17,47,0,48,31,49,0,50
%N A249738 a(n) = 0 if n is 1 or a prime, otherwise, when n = A020639(n) * A032742(n), a(n) = the largest k < A032742(n) such that either k = 1 or A020639(k) >= A020639(n), where A020639(n) and A032742(n) are the smallest prime and the largest proper divisor dividing n.
%H A249738 Antti Karttunen, <a href="/A249738/b249738.txt">Table of n, a(n) for n = 1..10000</a>
%F A249738 Other identities:
%F A249738 a(n) = A249744(n) / A020639(n).
%F A249738 a(k) = 1 if and only if k is one of A001248 (squares of primes).
%o A249738 (Scheme) (define (A249738 n) (cond ((or (= 1 n) (prime? n)) 0) (else (let ((lpf (A020639 n))) (let loop ((k (- (A032742 n) 1))) (cond ((= 1 k) k) ((>= (A020639 k) lpf) k) (else (loop (- k 1)))))))))
%Y A249738 Cf. A020639, A032742, A078898, A249744.
%K A249738 nonn
%O A249738 1,6
%A A249738 _Antti Karttunen_, Dec 06 2014